1. Field of the Invention
This invention relates to a slider for an optical head used for recording and/or reproducing information signals for a recording medium by exploiting a proximity optical field.
2. Description of the Related Art
For realizing a higher recording density of a recording medium, such as an optical disc, a technique has been proposed in which the proximity optical field is utilized for recording/reproducing the recording medium. In this technique, the numerical aperture NA of the optical system adapted for collecting light on the recording medium in recording/reproduction is adapted to be not less than unity (1) by exploiting the proximity optical field. This renders it possible to raise the recording density of the recording medium.
FIG. 1 shows an illustrative slider for an optical head used in recording/reproduction by exploiting the proximity optical field.
A slider for an optical head 100 includes an optical system employing a so-called solid immersion lens. The slider for the optical head 100 includes a slider member 105, supported by a suspension 103, a first optical lens 107 and a second optical lens 109. Both the first and second optical lenses 107, 109 are mounted on the slider member 105. When a recording medium 111, such as an optical disc, is run in rotation, the slider member 105 is uplifted by an air stream flowing between the recording medium 111 and the slider member 106 so as to be floated over the recording medium 111.
Of the optical lenses, loaded on the slider member 105, the first optical lens 107 arranged on the light incident side, is of the numerical aperture NA=0.6, while the second optical lens 109, arranged on the recording medium 111, is a semi-spherical lens with the refractive index n=2. Thus, an optical system combined from the first optical lens 107 and the second optical lens 108, is of the numerical aperture NA=1.2, thus achieving the numerical aperture NA&gt;1.
In recording/reproduction, the recording medium 111 is run in rotation to float the slider member 105 to maintain the interval of tens of a nm between the recording medium facing surface of the second optical lens 109 and the recording medium 111. The recording/reproducing light is caused to fall from the first optical lens 107 so as to be focussed on the recording medium facing surface of the second optical lens 109. At this time, evanescent light leaks from the recording medium facing surface of the second optical lens 109. This evanescent light, leaking from the recording medium facing surface of the second optical lens 109, is coupled to the recording medium 111. This evanescent light is used for recording/reproduction. Thus, with the numerical aperture NA&gt;1, it becomes possible to use an extremely fine light spot to perform recording/reproduction.
Meanwhile, in order to perform recording/reproduction as described above, the interval between the recording medium facing surface of the second optical lens 109 and the recording medium 111 needs to be sufficiently small as compared to the light wavelength. Thus, in this slider for the optical head 100, the slider member 105 is used to enable the interval between the recording medium facing surface of the second optical lens 109 and the recording medium 111 to be maintained at a sufficiently small value. There are a large number of prior art techniques for floating the head a minor amount. The slider for the optical head 100 exploits this technique routinely used in the field of hard disc devices.
In the slider for the optical head 100, shown in FIG. 1, the optical axes and the relative distance of the first optical lens 107 and the second optical lens 109 need to be aligned accurately, thus raising the problem of manufacture difficulties.
Also, in the present slider for the optical head 100, the recording medium facing surface of the second optical lens 109 constitutes a so-called air bearing surface (ABS) along with the recording medium facing surface of the slider member 105. Thus, with the present slider for the optical head 100, it is necessary to load the second optical lens 109 on the slider member 105 and to grind the recording medium facing surfaces thereof. However, with the conventional slider for the optical head 100, the second optical lens 109 and the slider member 105 are formed of different materials, such that it is difficult to grind these members to form the desired ABS surface to a high accuracy.
The recording medium facing surface of the slider member 105 is formed with a pattern of irregularities in order to control the air stream flowing between the slider member 105 and the recording medium 111 to realize stable floating. However, with the slider for the optical head 100, since the second optical lens 109 is exposed to the recording medium facing surface, the degree of freedom in designing the pattern of irregularities is lowered.
If the recording medium 111 is a magneto-optical disc, a magnetic field is required in recording/reproduction, so that a magnetic coil needs to be arranged in the vicinity of the light focussing point. This magnetic coil needs to be arranged so that the light focussing point will be at the center of the magnetic coil, while the magnetic coil needs to be buried in the slider member 105 so as not to disturb the floating of the slider member 105. However, since the second optical lens 109 is exposed to the recording medium facing surface, limitations are imposed on the burying position to lower the degree of freedom in designing. Although it may be contemplated to bury the magnetic coil in the second optical lens 109, it is difficult to bury the magnetic coil in the optical lens, thus increasing the manufacturing cost.
Thus, in the slider for the optical head 100, the optical axes and the relative distance of the first optical lens 107 and the second optical lens 109 need to be aligned accurately, thus raising manufacture difficulties. Also, the ABS surface is difficult to machine accurately, while the degree of freedom in designing is low. Moreover, limitations are imposed on the arraying position of the magnetic coil to lower the freedom in designing.